The present invention relates to the field of treatment of industrial and/or urban waste and more specifically to the thermolysis or pyrolysis of such waste.
Pyrolysis is a chemical decomposition of a body obtained by heating under absence of oxygen, whereas thermolysis is a decomposition obtained under the effect of a variation in temperature. These two terms thus define operations closely related to one another; this is the reason why they will be used equally hereafter.
Treating industrial and/or urban waste is notably important for the environment. The thermal treatment which has been most used in the past years is waste incineration, but the methods applied often pose problems, either at the level of the volume of solid product to be stocked, or at the level of the quality of the discharge.
As for the quality of the discharged products, several waste treatment plants have already been proposed in order to dispose of most of the pollutants, and notably heavy metals, chlorine, sulfur . . . in the gaseous effluents discharged as well as in the solid products generated by incineration.
A well-known technique disclosed in U.S. Pat. No. 4,303,477 consists in injecting in several places of a waste treatment circuit a basic powder for removing the heavy metals, sulfur dioxide or halogenated compounds from the combustion gases.
The applicant has proposed, in French patent application FR-2,668,774, a process and a plant for treating combustible waste according to which the waste is subjected to a pyrolysis operation. In order to produce, at the outlet of this plant, fuels as clean and valorizable as possible, the effluents resulting from the pyrolysis operation are subjected to a hot and dry treatment (that is without washing).
Besides, French patent application FR-2,654,112 describes a process and a plant for treating urban waste and implementing a thermolysis operation performed after a particular drying of the waste. Moreover, the tars initially present in the thermolysis gases are extracted from the thermolysis gases so as to allow these gases to be re-used later in the course of the process.
There are also other techniques recommending other types of treatments for the effluents and/or the particles resulting from the pyrolysis (or thermolysis) of the waste, but these post-treatments are generally either complex, and therefore costly, or little effective.